The invention relates to a method and a device for the state detection of a cutting device for agricultural crop.
Agricultural harvesting machines such as self-propelled forage harvesters are equipped with a chopping assembly that comprises a chopper drum that rotates opposite a stationary shear bar. Crop that reaches an engagement region formed by the chopper drum and the shear bar is fragmentized by the interaction of cutting blades, which are attached to the rotating chopper drum, with the shear bar.
The cutting blades become worn during operation. The cutting blades are therefore sharpened repeatedly, in order to attain a consistent cutting quality and minimize the cutting forces and, therefore, the drive energy required for chopping. Every time sharpening is performed, material is removed from the cutting blades when the dull cutting edges are sharpened. The result is that the distance between the cutting edges of the cutting blades and the shear bar changes. The chopping process is thereby impaired.
For the chopping process to be precise and energy-efficient, not only is knife sharpness important, but also the distance between the shear bar and the cutting tool. If the distance is too great, a portion of the incoming material may not be cut completely, and greater cutting forces may be required. If the distance is too small, there is a risk that the cutting blades and the shear bar will touch each other, which can result in material damage. Such touching also can cause material and/or entire machine elements to come loose, which is hazardous. A control unit that makes it possible to adjust the clearance position of the shear bar is therefore assigned to the shear bar.
In order to precisely adjust the shear bar using the control unit, for example, after sharpening, it must be possible to precisely detect the clearance position between the shear bar and the cutting tool. This is a technical challenge due, inter alia, to the close clearance, the high rotational speed and possible mechanical loads in the arrangement comprising the cutting tool and the shear bar.
Previously, the clearance between the shear bar and the cutting tool has been determined by moving the shear bar toward the rotating cutting tool until contact occurs, which can be detected by way of “knocking”, i.e. periodic contact noises caused by the cutting blades striking the shear bar. The shear bar is then moved away from the cutting tool out of the “contact position”, which is detected by knocking, by a certain extent in order to attain a defined clearance.
Although the contact noises produced in the approach are audible, the evaluation thereof by an operator is affected by highly subjective influences. A “knock sensor” is therefore used for detection purposes. The knock sensor is typically a vibration sensor (or a plurality thereof) mounted on the shear bar that detects “knocking” when a threshold value is fallen below. The knock signal therefore indicates that the cutting tool is in contact with the shear bar, on the basis of which a minimal shear bar clearance is deduced.
The disadvantage of this type of clearance determination is that only contact of the shear bar with the cutting tool is detected as such. What often happens, however, is that the shear bar is not oriented parallel to the cutting tool due to uneven wear of the cutting blades or the shear bar, due to loads on the shear bar, due to the shear bar being moved toward the cutting tool in a different manner at the sides, or due to other reasons. Upon movement toward the cutting tool, contact is only partial and the position thereof cannot be determined. It is not possible, therefore, to detect a deviation from the parallel orientation of the shear bar that is aimed for in the cutting process. The clearance position is therefore not set exactly.
In order to nevertheless attain a parallel orientation of the shear bar with respect to the cutting tool, EP 0 291 216 A1 provides that adjusting motors assigned to different ends of the shear bar are actuated individually in order to detect the knock signal generated when only one motor is actuated, at least on the side of the contact. The actual side on which contact takes place, therefore, is not detected, and erroneous detections can occur in practical application, in particular, in the presence of mechanical loads on the shear bar. In addition, a relatively great amount of time is required to actuate the adjusting motors individually.